India's main opposition Congress party has emerged victorious after elections in five key states across the country.

Congress swept to power in Kerala, Assam and Pondicherry, while a key ally took the southern state of Tamil Nadu.

State results

Assam

Congress 69

AGP-BJP: 42

Kerala

Congress+: 99

Left: 40

Pondicherry

Congress: 13

DMK: 12

Tamil Nadu

AIADMK+: 196

DMK+: 36

West Bengal

Left Front: 200

Trinamool+: 87

India's communists also won a record sixth term in West Bengal, continuing their reign as the world's longest serving elected communist administration.

The results are being seen as a major blow for Prime Minister Atal Behari Vajpayee whose BJP coalition partners have not won anywhere.

Congress president Sonia Gandhi said the outcome was a reflection on the working of the central government, and would "certainly" have an impact on it.

Correspondents say the elections will not have an immediate effect on Mr Vajpayee's government, because the BJP is not a key player in the five states.

But the polls have been presented as a litmus test for the BJP and could place strain on an already fractious alliance.

Bengal sees red

In the eastern state of West Bengal, speculation that a recently realigned alliance could pose a serious challenge to the communists faded away.

A record sixth term for the communists

Led by Buddhadev Bhattacharjee, the Left Front won an easy victory with 200 seats out of a total 294.

Their victory is being attributed to policies favouring the countryside and the urban poor.

"They have done a lot for us poor people. We can speak for the communists," Mamata Mandal, a slum-dweller, said.

The possibility of a similar hung assembly in Tamil Nadu was quickly ruled out.

The AIADMK alliance, led by the former film star Jayalalitha, won a resounding victory over the BJP's key government coalition partner, the DMK.

She was barred from running herself because of a bribery conviction.

Jayalalitha says she has a mandate to be chief minister

But as her alliance - which includes Congress - swept to victory in 196 seats out of 234, she declared she would take over as chief minister, a post she occupied between 1991 and 1996.

"People have given their mandate for me to rule the state.

"Putting anyone else in that place would mean disrespect to the verdict of the people. We cannot afford to do this," she told a television station.

BJP's woes

The results come as a setback to the prime minister's ruling BJP.

The governing coalition suffered a serious blow in March, when some of the BJP's partners demanded the resignation of Defence Minister George Fernandes over his alleged involvement in a bribery scandal.

"There is no doubt that the NDA [governing coalition] government in the centre is going to be further weakened," Congress party spokesman Anil Shastri told the BBC.

But as the results were coming in on Sunday, Mr Vajpayee dismissed claims that they would pose a threat to his government.